1. Field of the Invention
The present invention relates to a board printing system for printing solder paste on a board and for inspecting the printed state on the board.
2. Discussion of the Related Art
As equipment for producing boards each with a plurality of components mounted thereon, there are solder paste printing apparatus, component mounting apparatus, reflow apparatus and the like, and it is often the case that these apparatuses are connected by transfer devices to construct a board production line. Further, in order to inspect the printed state of solder paste on each board prior to mounting components in a component mounting apparatus, it has been conventional to provide a printing inspection apparatus of a stand-alone or dedicated type at a stage subsequent to the printing apparatus or to incorporate an inspection function in the printing apparatus. It has also been practiced to construct a component mounting line by arranging a plurality of component mounting apparatuses configured as modules in an in-line fashion and to make any printing inspection apparatus unnecessary by providing a component mounting apparatus at a forefront stage with an inspection function, thereby making the component mounting line a compact production line. As described above, the apparatuses which include a series of stages or steps to print solder paste on boards and to inspect the printed state of the boards can be grasped as a board printing system incorporated in the board production line.
Examples of the board printing system of this kind are disclosed in JP2006-286989 A (hereafter referred to as Patent Document 1) and JP2002-118360 A (hereafter referred to as Patent Document 2). The printing system in Patent Document 1 is provided with a printing apparatus and a board unloading device, and the printing apparatus is configured to switch a printing process interval per sheet of board in dependence on a lapse time after the cleaning of a printing member, while the board unloading device is configured to unload a post-printing board in harmonization with the processing timing at the next step. Further, as the next step, there is exemplified a construction that connects a printing inspection apparatus and a mounting apparatus in series. It is described therein that owing to a buffer function that the board transfer device performs in adjusting the unloading timing of the post-printing board, the tact time for the printing step and the next step can be adjusted.
Further, in a printing inspection method for cream solder disclosed in Patent Document 2, the printing is controlled to be discontinued when an abnormality at a printing step by the printing apparatus is detected. In Claim 2 of Patent Document 2, the occurrence of an abnormality is judged when the situation that a board is judged to have been printed incorrectly occurs more than a predetermined number of times. Further, Claim 7 of Patent Document 2 discloses a cream solder printing inspection apparatus which is provided with image pickup means, image processing means, image measuring means, abnormality judgment means and the like and which detects a printing abnormality based on image data to discontinue the printing operation. Further, in the description of an embodiment, there is disclosed a construction that a transfer device for the next step and an NG stocker for receiving each board at the occurrence of a printing abnormality are arranged at a stage subsequent to the printing inspection apparatus.
In board printing systems of this kind, it is difficult how to handle failure or rejected boards each of which is judge to be failure because of being not correct in the printed state. For example, in the printing system in Patent Document 1, the printing apparatus, the board transfer device, the printing inspection apparatus and the mounting apparatus are connected in series, and thus, when a rejected board is produced in the printing inspection apparatus, it is unavoidable that the production is discontinued to notify an operator as to the occurrence of the rejected board, so that the productivity goes down. If the rejected board were transferred together with corrected boards, it would be possible to continue the production. However, this would result in useless works because electronic components are mounted also on the rejected board.
In the printing inspection method and apparatus described in Patent Document 2, although the production can be continued until the NG stocker at the step subsequent to the printing inspection step receives rejected boards of a predetermined number of sheets, there is required an installation space for the NG stocker. Particularly, in a construction that an inspection function is incorporated in an electronic component mounting apparatus at a forefront stage of a modularized component mounting line, it is unavoidable to install the NG stocker between plural electronic component mounting apparatuses arranged in an in-line fashion. This results in spoiling the advantageous effects of the modularization, so that it becomes impossible to realize a production line which is compact in construction.
It is usual that the criterion for judging the printed state in a printing inspection apparatus is set strictly taking failsafe functions into consideration. Thus, it may be the case occasionally that even a rejected board which was judged to be rejected by the printing inspection apparatus can be used as a product through a correction judgment by the operator, and it also may be the case occasionally that such a rejected board can be used as a product by being given a minor reconditioning or correction by the operator. The correction in judgment or the reconditioning by the operator should be done within a limited time period in which printed solder paste still remain stable, and the board with which the correction judgment or reconditioning was made has to be returned into the production line. However, board production lines in the prior art have not been constructed to enable a board to be returned to the production line after being removed once therefrom. Thus, the operator has been required to take measures suited to the occasion such as, for example, temporarily stopping the board production line and then manually returning the board corrected in judgment or reconditioned to the board production line.